One known sorting machine includes a conveyor having a plurality of parallel sorting elements, the spacing of which increases across a sorting area. Individual elements are pivotally connected at each end to an endless roller chain by connecting links, with all of the connecting links being the same length. The elements also have a spigot projecting from each end. The machine further includes a pair of spaced worm gears of opposing helical pitch which run the length of the sorting area, with each worm gear having an increasing helical pitch from one end of the sorting area to the other. The spacing of the worm gears is such that the spigots of the sorting elements engage respective worm gears in the sorting area.
This machine has a complex conveyor drive system, wherein each roller chain is driven by a sprocket coupled to a gearbox and motor, and each gearbox also drives one of the worm gears. As the worm gears rotate in opposite directions to each other, they advance the sorting elements along the length of the sorting area. The spacing between adjacent sorting elements increases proportionally with the increase in helical pitch of the worm gears.
The main problem with this machine is the fact that the worm gears require careful and precise installation to ensure that the sorting elements remain parallel to each other along the length of the sorting area. This requires that each worm gear rotate at the same speed, and that corresponding loci on each opposed helix are directly opposite each other. These requirements are difficult, if not impossible, to achieve after the gearboxes and worm gears wear due to continued usage.
Another problem with this machine is that the worm gears generate forces in the sorting elements in directions both parallel to and normal to the line of travel of the elements. The normal forces increase friction and hence wear on the spigots of each of the sorting elements, and also the worm gears. If the spigots and worm gears are made from wear resistant materials, then the frictional forces increase, and there is an increased chance of the machine jamming. If the spigots and/or worm gears are made from low friction materials such as NYLON or TEFLON (both Trade Marks), then the amount of wear increases and sorting efficiency decreases due to the sorting elements moving from their parallel orientation to each other.
A yet further problem with this machine is the cost of manufacturing the opposed worm gears so that corresponding loci on each helix are directly opposite each other. The major component of this cost is due to the fact that the pitch of each helix increases from one end of the worm to the other, and this requires complicated and expensive machinery to produce.
Another sorting machine is described in British patent application no. 25399/75. In this machine, the sorting area is formed from an array of parallel grading rollers in the form of an endless driven loop. The rollers are mounted on T-shaped links within two parallel chains so that the spacing of the rollers depends on the path of the linking chains. Taking a straight path as the norm, pushing the chains into a convex path increases the roller spacing. Conversely, pushing the chains into a concave path reduces the roller spacing.
The path of the linking chains across the sorting area is determined by running each chain over a leaf spring, the curvature of which is adjusted to produce a suitable roller spacing.
The main disadvantage of this machine is that the spacing between the roller is substantially constant across the sorting area. Hence this machine will only separate out articles up to a particular size dependent on the roller spacing. If articles of several different sizes are required to be sorted from a quantity of bulk material, it is necessary to arrange a series of these machines with each successive machine having an increased roller spacing from the previous machine. Alternatively, if only one machine is used, the bulk material must be passed across the machine several times, with the roller spacing being increased for successive passes. Hence, while this machine is of comparatively simple construction, it has operational limitations when articles of several different sizes are required to be sorted from a quantity of bulk material.